FAIR VALUE - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	$ 4.1	$ 4.2
Debt maturing within one year	(38.0)	(28.0)
Related party loan	(1,077.4)	(1,008.6)
Long-term debt	(676.2)	(675.4)
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	4.1	4.2
Debt maturing within one year	(38.0)	(28.0)
Related party loan	(1,077.4)	(1,008.6)
Long-term debt	(758.5)	(782.4)
Foreign exchange forward contracts | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange forward contracts	0.9	(3.2)
Foreign exchange forward contracts | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange forward contracts	$ 0.9	$ (3.2)